Get ready for a 62-gun salute, let the fireworks and street parties commence: The royal baby has arrived, and it's a boy.

Prince William and Duchess Kate's first baby, a future monarch, was born today at 4:24 pm local time in London's private St. Mary's Hospital, the palace announced. The announcement said the baby weighed 8.6 pounds, and William was present for the birth.

The name was not immediately announced and may not be known for up to a week.

The news was supposed to be first announced in the traditional manner, on fancy paper with a Buckingham Palace letterhead on an easel at the palace front gates. But it was dark by the time the birth came, so the palace sent out an electronic press release first. The and the news went up on the royal Twitter feed and websites, proclaimed from every TV and computer screen in the country.

But great-grandmother Queen Elizabeth II was the first to get the news from her grandson, by encrypted phone to the palace, and just in time, too. She's scheduled to leave on her annual vacation at her Balmoral estate in Scotland at the end of this week.

In other words, the birth of the royal baby was a model of the careful blend of traditional and modern exemplified by this royal couple in the dozen years they've been a couple.

The baby arrives just short of 27 months since William and Kate were married in a spectacular ceremony at Westminster Abbey on April 29, 2011. The nine months of her pregnancy have been chronicled by the British and world media with excruciating detail and growing excitement about the first royal heir to be born in 31 years, since William himself was born to Prince Charles and Princess Diana.

(In fact, the last time the easel-and-note was used to announce a royal birth was for William.)

The baby moves immediately to third in line to the throne, behind father William and grandfather Charles. The queen is 87 and celebrating her 61st year on the throne.

The past few weeks saw rising royal-baby fever in Britain, with hopes high that the birth would provide an estimated $360 million boost in the flat British economy. Meanwhile, royal-baby doodads, such as Will and Kate masks, poured into shops for use at the street parties soon to break out all over the country.

The baby arrived , based on a mid-July due date. Unlike the majority of births in Britain, no one, not even the parents, knew the sex of the baby until the birth.

The baby was the second royal heir to be born in a London hospital, the same one where William was born in 1982 (as well as other recent royal babies not close in line to the throne). The Lindo Wing of St. Mary's is a favorite birthing destination of London's rich and famous, with estimates of the cost of a natural birth in a private suite as high as $15,000.

William was in the delivery room, as was his father when he was born. He is taking two weeks off for paternity leave.

Many details about the birth were unclear, and some of the speculation was a bit unseemly. Kate had planned a natural birth, being "not too posh to push," as the Daily Mail put it. Did she employ a "hypno-birth" or some other birthing strategy to dull pain? Will she breast-feed the baby?

It seems likely the couple will take the baby and stay for a few weeks at Kate's parents' estate in the country, where there is a nursery. The couple live in a small apartment at Kensington Palace when they're in London and are not expected to move into more palatial digs until the fall.

If they stay at the Middletons' mansion in Bucklebury, Berkshire, that would mark the first time a royal heir spent the first few weeks of life outside a royal palace or estate. These details matter to the British.

Britain learned that the duchess had gone into labor just minutes after she checked in and settled at the hospital. In the age of Twitter, it was considered impossible to keep the news under wraps for long, so the palace announced it. (The palace was forced to announce Kate was pregnant ahead of schedule when she experienced acute morning sickness early in her pregnancy and had to be hospitalized.)

Palace press officials had arranged for a theatrical ritual if the baby was born during daylight hours: After the birth, the formal notice, signed by her doctors, would be brought out the front door of the hospital, handed to a driver and then driven with a police escort through London to the front of Buckingham Palace, where it would be placed on the easel. The birth of a royal heir is rare enough to warrant the trouble, palace officials said weeks ago.

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Duchess in Labor: London-- At last, after weeks of waiting and on-the-edge anticipation (in a heat wave), the royal baby is ready to arrive. Duchess Kate of Cambridge is in the hospital and in the early stages of labor, Buckingham Palace confirmed early Monday.

"The Duchess traveled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with the Duke of Cambridge," tweeted Clarence House, the press office for Prince William and Catherine, the Duke and Duchess of Cambridge.

The couple's spokesman said, "Things are progressing normally" so far.

And not a moment too soon for everyone in the United Kingdom, from the queen and the prime minister down to each of the sweaty members of the media mob waiting for more than two weeks outside St. Mary's Hospital in Paddington.

Photographers paced back and forth outside the hospital in the mid-morning sun, on another hot day for London. Edward Cumming, 65, was sitting in the shade of a tree across from the entrance to the Lindo Wing.

"For one baby this seems a bit much," he said. "Although I guess you have to expect it for a royal baby."

Australian tourists Natasha and Diana (no last names or ages at their request) said they have been hanging around in London for about a week waiting for news of the royal birth, before heading to the British beauty spot of Cornwall in the far western edge of the island. When the news broke, they rushed over to see if they could spot anything. They couldn't, and were sitting in a shady spot wondering what to do next.

"We're kind of gutted it's happening today," Natasha said, before the two decided the wait for the baby was going to be too long and started making their way back toward Paddington station.

Kate and husband Prince William, both 31 and about to have their first baby, had been spending time at her parents' mansion about 50 miles away in rural Bucklebury, partly to escape the high temperatures (for London) in the city.

They had returned to Kensington Palace this weekend, according to the British media, although the palace had refused to confirm that, and said nothing until it confirmed she was in the hospital and in labor today.

She checked into the private Lindo Wing (Twitter jokesters had nicknamed it the "Limbo WIng" during what they called #GreatKateWait), where William and brother Prince Harry were born more than three decades ago.

And now everyone waits some more.

The palace said weeks ago that the duchess intends to have a natural birth, although that could change depending on circumstances. But the Cambridge press office is not discussing anything about that, nor whether labor was induced.

British reporters were reminding readers and followers that when William was born at St. Mary's 31 years ago, it was after about 16 hours of induced labor.

The palace had earlier planned to inform the world once she was in the hospital and started labor. As soon as the baby is born, William will call his grandmother, Queen Elizabeth II, on an encrypted call to let her know the news.

The queen joked this week, in answer to a child's question, that she hoped the baby would arrive soon because she's going on her annual vacation next week to her Balmoral estate in Scotland.

Meanwhile, if it's still daylight, a royal courier will emerge from the hospital and, with a police escort and a news helicopter clattering overhead, will head to Buckingham Palace to post a notice of the baby's gender, size and weight on an easel at the palace front gates.

Then the news will flood onto palace websites and social media and TV screens, and the celebrations will commence. Relief that it all went well will mix with joy, and pride that the British monarchy endures with another royal heir in hand.

This baby, whose name we will likely not learn for at least a few more days, will move to third-in-line to the throne, behind William at second and grandfather Prince Charles at first. Great-granny the queen is 87.

A girl would make for an especially historic royal baby, coming into the world with unprecedented expectations. For the first time in a 1,000 years of the English monarchy, the rules of succession have been changed so that birth order will trump gender. This princess of Cambridge, as she will be known, will be a future monarch even if she later has younger brothers.

The anticipation of the birth had built to a fever pitch, in part because it had been expected last weekend and nothing happened. This week, press reports had it, Prime Minister David Cameron, meeting with his Cabinet colleagues, was handed a note and gasped a little. Was it the royal baby? Nope, it was just a cricket score, and not a good one.

Today, he expressed the country's best wishes. "A very exciting occasion and the whole country is excited with them," he said. "So everyone is hoping for the best."

So it's big news for the Brits, certainly, and huge news for the world's ever-growing celebrity media universe, where celeb babies are click-magnets and royal babies even more so.

Which is why hundreds of journalists and photographers are still staking out St. Mary's: They're waiting for a first glimpse of the baby and parents when they emerge from the hospital.